Oxidation states of the manganese cluster during the flash-induced S-state cycle of the photosynthetic oxygen-evolving complex.

نویسندگان

  • T A Roelofs
  • W Liang
  • M J Latimer
  • R M Cinco
  • A Rompel
  • J C Andrews
  • K Sauer
  • V K Yachandra
  • M P Klein
چکیده

The Mn K-edge x-ray absorption spectra for the pure S states of the tetranuclear Mn cluster of the oxygen-evolving complex of photosystem II during flash-induced S-state cycling have been determined. The relative S-state populations in samples given 0, 1, 2, 3, 4, or 5 flashes were determined from fitting the flash-induced electron paramagnetic resonance (EPR) multiline signal oscillation pattern to the Kok model. The edge spectra of samples given 0, 1, 2, or 3 flashes were combined with EPR information to calculate the pure S-state edge spectra. The edge positions (defined as the zero-crossing of the second derivatives) are 6550.1, 6551.7, 6553.5, and 6553.8 eV for S0, S1, S2, and S3, respectively. In addition to the shift in edge position, the S0--> S1 and S1--> S2 transitions are accompanied by characteristic changes in the shape of the edge, both indicative of Mn oxidation. The edge position shifts very little (0.3 eV) for the S2--> S3 transition, and the edge shape shows only subtle changes. We conclude that probably no direct Mn oxidation is involved in this transition. The proposed Mn oxidation state assignments are as follows: S0 (II, III, IV, IV) or (III, III, III, IV), S1 (III, III, IV, IV), S2 (III, IV, IV, IV), S3 (III, IV, IV, IV).

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عنوان ژورنال:
  • Proceedings of the National Academy of Sciences of the United States of America

دوره 93 8  شماره 

صفحات  -

تاریخ انتشار 1996